Exhaust gas recirculation (EGR) is a technique that may reduce NOx (e.g., nitrogen oxide and nitrogen dioxide) gases in an exhaust stream produced by diesel turbocharged engines. EGR works by recirculating a portion of the exhaust gas flow discharged by an engine back to the cylinders of the engine. The overall combustion process is thereby slowed and cooled. As NOx gases are more readily formed at higher temperatures, the formation of NOx gases may thus be reduced. Errors in the flow of recirculated gas, however, may cause various issues. For example, the introduction of higher amounts of recirculated exhaust gas may result in retarded engine performance while lower amounts may increase NOx gas formation and the creation of engine ping.
Metering of the amount of recirculated gas processed by an EGR system may be achieved in part by measuring the overall volumetric flow rate of recirculated gas through the system. Typically, this measurement may be made by passing the entire recirculated gas flow stream through an orifice that is formed by an orifice plate and measuring the resulting pressure drop across the plate. An overall EGR volumetric flow rate may then be calculated via application of Bernoulli's equation, for example.
Such orifice plate flow measurement configurations may introduce excessive flow restriction to an EGR system and may therefore require that a larger orifice be utilized to ameliorate flow restriction effects. With larger orifice diameters, however, the capability of such a configuration to accurately measure a pressure drop across the orifice at lower volumetric flow rates is reduced, and overall packaging issues may arise in the engine compartment.
The inventors herein have realized that a flow measurement configuration that decreases restriction to flow and allows for a larger dynamic flow measurement range may be advantageous. In one approach, a method for measuring exhaust gas recirculation flow in an engine is provided. The method comprises separating EGR flow into at least a first flow and a second flow, passing the separated first flow through a restriction region, where the first flow passes through the restriction region separately from the separated second flow, combining the separated second flow and inducting the combined flows into a cylinder of the engine, where the EGR flow is separated and then combined within a common EGR passage.
In this way, it may be possible to maintain sufficient dynamic measurement range (for higher and lower EGR flows), while reducing overall EGR restriction. Thus, desired overall EGR system packaging may be achieved.
Note that various approaches may be used for separating the EGR flow, such as dividing a tubular passage of the EGR system, providing a plurality of EGR passages, etc. Further, note that various restrictions may form the restriction region, such as via an integrated or separately formed orifice. Finally, note that the common EGR passage may be a common tubular assembly, separate tubes coupled together via various valves, etc.
In another approach, another method for measuring exhaust gas recirculation (EGR) flow in an engine may be used. The method may comprise: separating EGR flow into two separated flows including a first separated flow and a second separated flow; passing the separated first flow through a flow restriction region, where the first flow passes through the flow restriction region separately from the second flow; combining the first and second separated flows and inducting the combined flows into a cylinder of the engine, where the EGR flow is controlled by a common EGR valve, and where the second separated flow includes a greater mass flow than the first separated flow; and correlating the first separated flow to the combined flow and adjusting the EGR valve in response thereto.
In this way, accurate control of both higher and lower EGR flows through the EGR valve can be achieved, while reducing impacts on engine packaging in the engine compartment.